Animal residuals from large concentrated animal feeding operations present unique problems for farm operators. The main problems relate to odor control and residual disposal. The residuals from hog operations consist mainly of feces, urine, hair, skin, spilled feed and water, and wash or flush water. The residuals mixtures are the major source of intense odor. The intensity of the odor increases with the age of the residuals. Water pollution is also a problem caused mainly when residuals are improperly land applied.
In many intense operations, animals such as hogs are confined in buildings. The animal residuals (manure) accumulate in the confined feeding and growing building until they are removed, typically by flushing with water or mechanical scraping. Mechanically scraped residual, while requiring more labor, is typically more concentrated, and the lower volume is desirable for storage and land application. A process for mechanical removal and processing of solid waste from cattle feed lots is described by Lynn in U.S. Pat. No. 3,973,043. The solid waste is collected and mixed with water to form a slurry that contains at least about 10 parts by weight of solid material, but can contain much higher solids concentration so long as the slurry can be easily pumped. This slurry then undergoes anaerobic fermentation to produce a methane gas stream and a residue material. The residue material may be used as a fertilizer, or subjected to an aerobic fermentation to produce a protein rich product usable in animal feed and a residue useful as soil fertilizer component. The inventor states that about 20% by weight of the solid material in the slurry is converted to vapor each day, so that the residence time in the anaerobic vessel is about 5 days when the system is in continuous operation. Residence time in the aerobic process may be about 10 to 14 days.
In the treatment of hog waste, water flushing is the common practice because of the decreased labor requirement. Unfortunately frequent water flushing increases the volume of water and wastes that have to be handled, so the amount of water used is minimized as much as possible. Typically the flushed residual is stored in earthen ponds or lagoons. The material in the lagoons is too dilute for significant anaerobic digestion and does not result in adequately treated waste. Lagoons are also sources of unpleasant odors, as the liquid is allowed to evaporate or is applied as irrigation. Thus the operator is faced with the choice of flushing less frequently, which results in more intense odor in the feeding and growing buildings, or more frequent flushing, which compounds the lagoon odor problems. Lagoons also present the risk of subsurface leakage that may contaminate drinking water supplies.
Enclosed storage and treatment facilities for odor control, such as are used in municipal treatment plants are too expensive to be practical for an agricultural operation. Therefore, confined growing/feeding operators (especially hog operations) typically utilize some type of lagoon system for handling of animal waste. There is a need, therefore, for an economical system for handling the animal waste from an intense feeding operation, especially the growing of hogs, that does not utilize open lagoons and that does not result in offensive odors from infrequent flushing of feeding/growing barns.
The present disclosure addresses the problems of the art by providing systems and methods for total management of liquid and solid animal wastes to control odor emissions and to prevent pollution of land and water resources. The present disclosure provides additional advantages over the art, including the ability to accommodate a high volume of water, allowing the flushing of a typical barn on at least a daily basis. This allows the removal of fresh residuals before intense odor can be generated. The anaerobic digester is enclosed so that odors are not released, and methane produced by fermentation may be captured and utilized for energy. The liquid fraction is further treated by aerobic digestion to remove organic compounds, further reducing the odor of the treated water. This water can then be recycled as high volume flush water to remove fresh residuals without causing an odor problem, and excess water is also available for irrigation. There is about a 60% reduction in dry weight of the solids in the disclosed system and the transformed remaining solids do not produce intense odors and may therefore be used for land applications.
In certain preferred embodiments, the invention may be described as a system for treating animal waste, and includes the anaerobic digester(s), clarifiers and aerobic reactors configured such that the waste may be first subjected to enclosed anaerobic digestion followed by moving a liquid portion to an aerobic reactor and using clarified liquid from the aerobic reactor to flush a barn and restart the cycle. Although a preferred embodiment of such a system is described in Example 1, the system may be adapted to feeding barns designed to hold greater or few numbers of animals, either by reducing the size of the tanks, or by adding additional or larger tanks as needed. It is also understood that two or more barns may be connected to a single system, or a plurality of barns may be configured to each be connected to its own system individually. The specific systems described herein as preferred embodiments are directed to production of hogs because of the problems presented by intense hog raising and because of the high liquid content of hog waste. It is understood, however, that flush barns that are used to raise other species of domestic or farm animals or birds would also benefit from the described technology. Other animal species would include, but are not limited to beef or dairy cattle, sheep, goats, chickens, turkeys, or ratites. All such variations of the waste treatment systems are contemplated herein and fall within the scope and spirit of the appended claims.